* {
  box-sizing: border-box;
}

body {
  background-image: linear-gradient(90deg, #ffbf5f, #7158e2);
  font-family: 'Roboto', sans-serif;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
  overflow: hidden;
  margin: 0;
}

/* 点开前 */
.search {
  position: relative;
  height: 50px;
}

/* 点开以后 */
/* 做一个动画效果，看起来更加顺眼 */
.search .input {
  background-color: #fff;
  border: 0;
  font-size: 18px;
  padding: 15px;
  height: 50px;
  width: 50px;
  transition: width 0.3s ease;
}

.btn {
background-color: #fff;
border: 0;
cursor: pointer;
font-size: 24px;
position: absolute;
top: 0;
left: 0;
height: 50px;
width: 50px;
transition: transform 0.3s ease;
}

.btn:focus,
.input:focus {
outline: none;
}

.search.active .input {
  width: 200px;
}

.search.active .btn {
  transform: translateX(198px);
}